Hybrid coating compositions

ABSTRACT

The present invention provides a composition for use in forming an abrasion-resistant easy-to-clean coating on a substrate. The composition according to the invention includes a mixture of a fluorocarbon polymer component and an enamel-forming component. The enamel-forming component includes at least a first lead-free and cadmium-free glass frit. The first lead-free and cadmium-free glass frit includes from about 30% to about 50% P 2 O 5 , from about 15% to about 30% Al 2 O 3 , and from about 2% to about 40% X 2 O where X=Na and/or K. The present invention also provides a method of forming an abrasion-resistant easy-to-clean coating on a substrate. The method includes applying the composition according to the invention to a substrate and sintering the applied composition to fuse an abrasion-resistant easy-to-clean coating to the substrate. The method can be used to apply the composition to a variety of substrate materials such as metals, glass, ceramics, and stone, using a variety of application techniques such as wet spraying, screen printing, electrophoresis, dry electrostatic deposition, wet dipping, and flow coating.

FIELD OF INVENTION

The present invention provides a composition for use in forming anabrasion-resistant easy-to-clean coating on a substrate, and a method offorming an abrasion-resistant easy-to-clean coating on a substrate.

BACKGROUND OF THE INVENTION

Fluorocarbon polymers, such as, for example, polytetrafluoroethylene(PTFE), polymers of chlorotrifluoroethylene (CTFE), ofhexafluoropropylene (HFP), fluorinated ethylene-propylene copolymers(FEP), and polyvinylidene fluoride (PVDF), are known to have superiornon-stick properties. For this reason, they have been used in a widevariety of applications, including forming non-stick coatings onarticles of cookware, bakeware, iron sole plates, food contactingsurfaces of small appliances, snow shovels and plows, chutes andconveyors, saws, hoppers, and other industrial containers. However, dueto the inherent non-stick nature of these and other fluorocarbonpolymers, it has been difficult to form non-stick coatings that adherewell to substrates such as metals and ceramics. Moreover, due to theinherent softness of fluorocarbon polymers, it has been difficult toform non-stick coatings that resist abrasion.

In an effort to overcome these difficulties, it has been theconventional practice to apply one or more base coats containingadhesive resins in order to better adhere fluorocarbon polymer top coatsto substrates (throughout this specification and in the claims, theterms “base coat” and “primer coat” are used interchangeably). Ingeneral, such base coats comprise a combination of high temperaturebinder resins, such as polyamideimide resins, polyethersulfone resins,or polyphenylene sulfide resins, and fluorocarbon polymer resins. Theperformance of these conventional non-stick coating systems is basedupon a stratification of the applied coatings. This stratificationresults in a coating that is rich in high temperature binder on thebottom and rich in fluorocarbon polymer at the top. The binder-richbottom provides adhesion to the substrate while the fluorocarbonpolymer-rich top provides a layer to which subsequent fluorocarbonpolymer top coats can be fused by sintering at high temperature.

The performance of such non-stick coating systems is at best acompromise. The bottom layer of the base coats is not a purely binderresin. Considerable levels of fluorocarbon polymer resins must beincluded in the base coats in order to provide a layer that issufficiently rich in fluorocarbon polymer to promote good bonding ofsubsequent fluorocarbon polymer top coats to the base coat. The presenceof fluorocarbon polymer resins in the base coat are disadvantageousbecause they detract from the adhesion of the base coat to thesubstrate. Therefore, it has been necessary to roughen substrates bymechanical (e.g. grit blasting) or chemical (e.g. etching) means toassist holding the base coat to the substrate.

Moreover, because both the adhesive resins and fluorocarbon polymers arerelatively soft, there have been difficulties in making these non-stickcoatings resistant to abrasive wear. Efforts to overcome thesedeficiencies have included the addition of mica particles, ceramicfillers, or metal flakes to the intermediate and top coat in order toincrease the hardness. The presence of these fillers can bedisadvantageous. For example, incorporation of metal flakes in theapplied coatings can actually promote chemical corrosion of theunderlying metal substrate due to dissimilarity between the metals.Moreover, these particulate fillers cannot be incorporated into thenon-stick coating at high levels because at high levels they diminishthe non-stick properties of the coating and the bonding to thesubstrate.

Due to the limitations thus described, articles of cookware coated withconventional fluorocarbon polymer non-stick coating systems are prone todamage and abrasive wear during normal use. Cooking utensils, forexample, often cause cuts, slices, or gouges in the non-stick coatingwhich permit acids or alkaline foodstuffs and cleaning agents topenetrate to the exposed substrate and cause corrosion. Corrosion of theunderlying substrate by these materials can further weaken the adhesionof the non-stick coating adjacent to the cut or slice. Moreover,abrasive forces routinely encountered in cooking and cleaning cause thegradual removal of the soft fluorocarbon polymer top coat resulting indiminished non-stick properties. Conventional non-stick coatings simplydo not adequately protect the substrate from corrosion or thefluorocarbon polymer top coat from routine abrasive wear.

Compositions are known for use in forming porcelain enamel coatings thatare very resistant to abrasion and chemical wear. Unfortunately, suchknown porcelain enamel coatings do not possess non-stick propertiescomparable to fluorocarbon polymer coatings. Moreover, such knownporcelain enamel coatings are generally not considered to possess socalled “Easy-to-Clean” properties. Despite considerable effort, pastattempts to formulate a composition that can be used to form a coatingon substrates that exhibits the excellent non-stick attributes offluorocarbon polymer coatings as well as the abrasion resistance ofporcelain enamels have heretofore been largely unsuccessful.

SUMMARY OF INVENTION

The present invention provides a composition for use in forming anabrasion-resistant easy-to-clean coating on a substrate. The compositionaccording to the invention comprises a mixture of a fluorocarbon polymercomponent and an enamel-forming component. The fluorocarbon polymercomponent can comprise one or a blend of polymers that are either fullyor partially fluorinated. Polymers and copolymers containing PTFE arepresently most preferred. The enamel-forming component comprises atleast a first lead-free and cadmium-free glass frit comprising by weightfrom about 30% to about 50% P₂O₅, from about 15% to about 30% Al₂O₃,from about 2% to about 40% X₂O where X=Na and/or K.

The present invention also provides a method of forming anabrasion-resistant easy-to-clean coating on a substrate. The methodcomprises applying a composition according to the invention to asubstrate and sintering the composition to form and fuse anabrasion-resistant easy-to-clean coating to the substrate. Thecomposition can be applied to substrates using a variety of applicationtechniques such as wet spraying, screen printing, electrophoresis, dryelectrostatic deposition, wet dipping, and flow coating.

Coatings formed using the composition and method according to thepresent invention are abrasion-resistant and easy-to-clean. Suchcoatings exhibit excellent acid resistance and are hydrophobic. Variouspigments and colorants can be added to the composition to produce a widevariety of colored coatings including, but not limited to, black, grey,green, blue, and brown. Alternatively, one or more color-producingmetallic oxides can be added to the glass component during smelting toimpart color to the coating. The color of the coatings can be made to bevery dark to very light depending upon the amount and type of colorantused. The sintered coating is stain resistant.

The composition can be applied to coat a variety of substrate materialssuch as, for example, metals, glass, ceramic, and stone. The coating canbe applied to a wide variety of products, including cookware, exteriorand interior surfaces of appliances such as ranges, ovens, washingmachines, and dishwashers, sanitary ware, and architectural productssuch as galvanized steel panels, terra cotta roofing tiles, and masonry.

The foregoing and other features of the invention are hereinafter morefully described and particularly pointed out in the claims, thefollowing description setting forth in detail certain illustrativeembodiments of the invention, these being indicative, however, of but afew of the various ways in which the principles of the present inventionmay be employed.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The novel composition according to the present invention is particularlyuseful for forming an abrasion-resistant easy-to-clean coating on asubstrate. Throughout the specification and in the appended claims, theterm “abrasion-resistant” means that the applied sintered coating isremoved at a rate of less than 10.0 g/m² according to the PEI TABERmethod (1500 cycles), and the term “easy-to-clean” means that theapplied sintered coating scores 20 or better (Class A) according to theEasy-To-Clean Test (FAN Procedure), which is described in detail below.

The composition according to the present invention comprises a mixtureof a fluorocarbon polymer component and an enamel-forming component. Theterm “mixture” describes the physical blend of the fluorocarbon polymercomponent and the enamel-forming component that comprise thecomposition. The term “mixture” is not intended to suggest that there isany chemical reaction between the two components, which probably doesnot occur. The fluorocarbon polymer component comprises less than about50% by weight of the composition, and preferably from about 2.5% byweight to about 30% by weight of the composition. The enamel-formingcomponent comprises at least about 40% by weight of the composition, andpreferably from about 50% by weight to about 97.5% by weight of thecomposition.

The fluorocarbon polymer component comprises one or a blend of polymersand/or copolymers that are either fully or partially fluorinated. Fullyfluorinated polymers suitable for use in the invention include polymersand copolymers of tetrafluoroethylene (TFE), perfluoromethylvinylether(PMVE) and perfluoropropylvinylether (PPVE), such as, for example, PTFE,modified PTFE, perfluoroalkoxy polymers such as PMVE-TFE copolymer(sometimes referred to herein as MFA) and PPVE-TEF copolymer (sometimesreferred to herein as PFA). Partially fluorinated polymers suitable foruse in the invention include polymers and copolymers of PVDF, CTFE, andmodified PTFE. PTFE polymers and/or copolymers containing PTFE arepresently most preferred for use in the invention because such polymersand copolymers possess excellent properties (e.g., they are hydrophobic,non-toxic, and non-sticky) and do not degrade at the temperatures of useand sintering.

Depending upon the application technique to be used to form the coating,the fluorocarbon polymer component can be mixed with the enamel-formingcomponent while dispersed in a liquid or as a dry solid powder. In apreferred embodiment, the fluorocarbon polymer component comprises anaqueous dispersion of PTFE, MFA, PFA, and/or modified PTFE. Preferably,the fluorocarbon polymers in these aqueous dispersions have an averageparticle size within the range of from about 50 nm to about 10 microns,and more preferably within the range of from about 150 nm to about 10microns. It will be appreciated that such dispersions can have a bimodalor multi-modal particle size distribution.

The enamel-forming component comprises at least a first lead-free andcadmium-free glass frit. Throughout the specification and in theappended claims, the term “lead-free and cadmium-free glass frit” meansthat no PbO and/or CdO is intentionally added during production of theglass, and that the total amount of PbO and/or CdO in the fritted glassis less than about 0.1% by weight.

The first lead-free and cadmium-free glass frit comprises by weight fromabout 30% to about 50% P₂O₅, from about 15% to about 30% Al₂O₃, and fromabout 2% to about 40% X₂O where X=Na and/or K. Thus, the first lead-freeand cadmium-free glass frit can be characterized as an aluminumphosphate glass frit. Various aluminum phosphate glass frits can be usedas the first lead-free and cadmium-free glass frit in the inventionprovided they meet the previously stated compositional ranges.

The first lead-free and cadmium-free glass fit preferably comprises byweight from about 30% to about 50% P₂O₅, from about 15% to about 30%Al₂O₃, from about 2% to about 40% X₂O where X=Na and/or K, up to about12% B₂O₃, up to about 10% ZnQ, up to about 8% SiO₂, up to about 5% Li₂O,up to about 3% MnO, up to about 3% CoO, up to about 3% NiO, up to about3% CuO, up to about 3% Sb₂O₃, up to about 3% Fe₂O₃, and up to about 3%MoO₃. The first lead-free and cadmium-free glass frit can also compriseby weight up to about 15% fluorine above the weight of the othercomponents in the frit.

The first lead-free and cadmium-free glass frit can be smelted in allknown types of smelters, including continuous, rotary, electrical, andinduction smelters. Typically, selected oxides are smelted attemperatures of from about 1200° C.±100° C. for about 30±10 minutes.Smelting temperatures and times will vary considerably depending uponthe composition of the frit. The molten glass is then converted to glassfrit using water-cooled steel rollers or water quenching. It will beappreciated that the step of producing the first lead-free andcadmium-free glass frit is not per se critical and any of the varioustechniques well-known to those skilled in the art can be employed.

The enamel-forming component of the composition according to theinvention can further comprise one or more additional lead-free andcadmium-free aluminum phosphate glass frits. Additional glass frits canbe used to improve bonding and acid resistance. Preferably, theenamel-forming component comprises from about 60% to about 100% byweight of the first lead-free and cadmium-free glass fit and up to about40% by weight of a second lead-free and cadmium-free glass frit orcombinations of the second lead-free and cadmium-free glass frit andother lead-free and cadmium-free aluminum phosphate glass frits. Thesecond lead-free and cadmium-free glass frit preferably comprises byweight from about 30% to about 50% P₂O₅, from about 2% to about 40% X₂Owhere X=Na and/or K, from about 10% to about 30% Al₂O₃, up to about 12%SiO₂, up to about 8% B₂O₃, up to about 5% Li₂O, up to about 5% NiO, upto about 4% MnO, up to about 3% CoO, up to about 3% CuO, up to about 3%Sb₂O₃, up to about 3% Fe₂O₃, and up to about 3% MoO₃. The secondlead-free and cadmium-free glass frit can also comprise by weight up toabout 15% fluorine above the weight of the other components in the frit.The second lead-free and cadmium-free glass frit can be produced in thesame manner as the first lead-free and cadmium-free glass frit.

The composition can also include one or more pigments and/or milladditions, which are typically, but not necessarily, milled togetherwith the enamel-forming component. Suitable pigments and mill additionsinclude, for example, titanium dioxide, inorganic pigments, potassiumhydroxide, sodium metasilicate, sodium silicate, clay, quartz,bentonite, magnesium carbonate, potassium nitrite, sodium aluminate, andboric acid. Inorganic materials, such as silica, zirconia, alumina,spodumene, and feldspar, can also be added to the composition in orderto modify the texture and/or to adjust the roughness of the sinteredcoating. Inorganic oxides (pigments) used to color the composition canbe added so as to comprise up to about 20% by weight of the solidsportion of the composition without significantly degrading the desiredproperties in the sintered coating. Other mill additions, such astexture enhancers and pH adjusters, preferably comprise up to about 10%by weight of the solids portion of the composition. It will beappreciated that the selection of pigments, and/or mill additions mustbe made in view of the technique by which the composition is to beapplied to a substrate and the desired texture and/or color of thesintered coating.

The composition according to the invention can further comprise avehicle. Suitable vehicles include, for example, water and organicvehicles such as pine oil. It will be appreciated that the type andamount of vehicle used in the composition is not per se critical, andthat the selection of a vehicle will depend on the particular techniquebeing employed to apply the composition to the substrate.

The present invention is also directed to a method of forming anabrasion-resistant easy-to-clean coating on a substrate. The methodcomprises providing a substrate; providing a composition for use informing an abrasion-resistant easy-to-clean coating on a substrate aspreviously described; applying the composition to the substrate; andsintering the composition to fuse the coating to the substrate. Suitablesubstrate materials include metals, glass, ceramic, and stone.

Metal substrates do not have to be pretreated prior to application ofthe composition. The composition can be applied to: steel, including hotrolled steel, enamel ground-coated steel, aluminized steel, picklednickel-coated steel, stainless steel, and galvanized steel; cast iron;aluminum, including alloys of aluminum, enamel base-coated aluminum, andaluminum-containing surfaces coated with the composition described in WO00/56537; and copper, including alloys of copper. Although it is notnecessary in most instances, the metal surface can be pretreated toenhance adhesion. Such pretreatment can include for example, grit orsandblasting, phosphating, and acid or aklaline degreasing.

Application of the composition to the substrate can be accomplished by avariety of application techniques including, for example, wet spraying,screen printing, electrophoresis, dry electrostatic deposition, wetdipping, and flow coating. Sintering is preferably accomplished byheating the applied composition to a temperature of from about 400° C.to about 580° C. for about 2 to about 25 minutes. During sintering, thefluorocarbon polymer melts. It will be appreciated that sinteringtemperatures and times will vary depending upon the thickness of theapplied composition and the characteristics of the substrate to which ithas been applied.

If too much fluorocarbon polymer is present in the composition (i.e.,more than about 50% by weight), the coating can easily become overtiredduring sintering, which results in rapid deterioration of the sinteredcoating. While it is possible to adjust the firing conditions to avoidsuch deterioration during sintering, the mechanical properties of theresulting coating are less than desired. Conversely, if too littlefluorocarbon polymer is present in the composition (i.e., less thanabout 1.0% by weight), the sintered coating usually does not possesssome of the desired properties, such as hydrophobicity and easiness toclean. Thus, the amount of fluorocarbon polymer present in thecomposition is preferably within the range of from about 2.5% to about35% by weight.

Coatings formed using the composition and method according to thepresent invention are abrasion-resistant and easy-to-clean. Suchcoatings exhibit excellent acid resistance and are hydrophobic. Byincorporating various pigments and colorants in the composition, a widevariety of colored coatings can be produced including, but not limitedto, black, grey, green, blue, and brown. Such colored coatings can bemade to appear very dark to very light depending upon the amount andtype of colorant used.

The coating can be applied to a wide variety of products. The coating isparticularly useful for application to cookware because it isscratch-resistant and provides excellent food release properties. Thecoating can easily withstand conventional cooking temperatures, resistsstaining, and is not damaged when subjected to many dishwashing cycles.

The composition is also useful for application to exterior and interiorsurfaces of appliances such as ranges, ovens, washing machines, anddishwashers. The coating can be formed so as to provide a very glossyappearance that is not adversely affected by repeated exposure to hightemperatures conventionally generated in such appliances. Because of itsexcellent abrasion-resistance and food contact resistance, the coatingis particularly suitable for application to the interior surfaces ofoven cavities, cooking hobs, range tops, and burner grates.

The coating can also be applied to sanitary ware, such as bathtubs andsinks. The coating resists staining, is very durable, and is detergentand water resistant. Additionally, the coating can be applied toarchitectural products such as galvanized steel panels, terra cottaroofing tiles, and masonry. The coating can be used to seal porousproducts and provide a surface that is graffiti resistant.

The sintered coating preferably exhibits an acid resistance of A orbetter according to ISO 2722, a hardness of 5 or better on the Mohsscale, and is removed at a rate of less than 10.0 g/m² according to thePEI TABER method (1500 cycles). In addition, the sintered coatingpreferably exhibits a score of 20 or better according to theEasy-To-Clean Test (FAN Procedure), and a score of 4 N or betteraccording to the Scratch-Resistance Test (NEN 2713). Several of thesetesting methods are discussed below:

Easy-To-Clean Test (FAN Procedure)

The Easy-To-Clean Test, which is also known as the FAN Procedure, isused to objectively measure the ease with which baked-on foods can beremoved from a coating. The letters “FAN” are an abbreviation of theFrench phrase facile a nettoyer, which translates to English as“easy-to-clean.” In this test, samples of the following foods areseparately applied at room temperature to coated 10 cm×10 cm couponsthat are also at room temperature: ketchup; lemon juice; salted milk (4g of salt per liter of milk); fresh egg yolk; and Viandox (meat juice).Raschig rings are attached to the coated coupons using SILICOMET JT545silicone adhesive. A 1 g sample of each food is placed within each ringon the surface of the coated coupon. The coupons are then placed into apreheated oven and heated for 30 minutes at 250° C. The coupons are thenremoved from the oven and allowed to cool to room temperature. TheRaschig rings and silicone adhesive are then removed from the coatedcoupons and each coupon is wiped 6 times with the abrasive side of a wetVileda Graffix sponge using the same force (the brand of sponge is notper se critical, and any common household sponge that has an abrasiveside and a non-abrasive side can be used). The temperature of the waterretained in the sponge is preferably about 40° C. The coupon is giventhe highest score at which all of the baked-on food can be removedaccording to the following scoring system:

Step Cleaning Method Pressure Score 1 Surface of coupon completelycleaned 1 kg 5 by wiping with abrasive side of sponge. 2 Surface ofcoupon completely cleaned 3 kg 4 by wiping with abrasive side of sponge.3 Surface of coupon completely cleaned 6 kg 3 by wiping with abrasiveside of sponge. 4 Surface of coupon completely cleaned 6 kg 2 by wipingwith abrasive side of sponge and more detergent. 5 Food residue remainson surface of 6 kg 1 coupon even after wiping with abrasive side ofsponge and more detergent.

The score for all five foods is summed, and the coating is given aclassification according to the following scale:

Total Class  5 to 9 points D 10 to 14 points C 15 to 19 points B 20 to25 points A

Scratch-Resistance Test (NEN 2713)

The Scratch-Resistance Test (NEN 2713) is used to objectively measurethe ability of an applied coating to resist scratching. In this test,coated 10 cm×10 cm coupons are fixed to the turntable of an Erichsen413D Scratch Resistance Tester. The stylus is placed against the surfaceof the coupon at an initial load of 10 N and the coupon is rotated onecomplete turn. Next, the stylus is placed about 2 mm closer to thecenter of the coupon, the load on the stylus is decreased, and thecoupon is rotated one complete turn. A number of cycles/scratches aremade with ever decreasing loads (the number of cycles is usually 12 orless) until the load on the stylus has been decreased to 0.1 N.

After the scratching has been completed, the coupon is cleaned by wipingwith a clean dry paper towel. Each quadrant of the scratched coupon isthen seperately colored using a felt tip pen. The felt pens contain red,blue, black, and green inks, respectively, that provide a surfacediscoloration of less than about ΔE=10 (Cielab colorimetric values)after dry wiping on unscratched coated surfaces. After the inks havedried (at least one minute), the quadrants the inks are wiped from eachquadrant using a separate dry clean paper towel. The coupons are thenvisually examined at a distance of 25 cm. The scratch resistance isreported as the last highest load at which less than 50% of the ink wasretained within a circular scratch for any of the colors.

The following examples are intended only to illustrate the invention andshould not be construed as imposing limitations upon the claims.

EXAMPLE I

Lead-free and cadmium-free aluminum phosphate glass frits A and B wereprepared by smelting selected oxides (and an additional amount by weightof F and NO₂ above the weight of the oxides) in a smelting pot. GlassFrit A was smelted at about 1200° C. for about 30 minutes. Glass Frit Bwas smelted at about 1150° C. for about 30 minutes. In both cases, themolten glass was converted to frit using water cooled rollers. The fritshad the following composition in weight percent:

Component Frit A Frit B P₂O₅ 39.57 40.85 Al₂O₃ 24.68 20.95 Na₂O 17.9120.94 B₂O₃ 5.28 2.51 K₂O 4.41 0 SiO₂ 2.34 6.07 ZnO 2.95 0 Li₂O 1.31 1.05NiO 0.49 2.40 MnO 0.37 1.84 CoO 0.22 1.05 Fe₂O₃ 0.20 0.95 CuO 0.10 0.52Sb₂O₃ 0.10 0.52 MoO₃ 0.07 0.37 F* 5.63 8.06 NO₂* 2.35 2.62 *NOTE: As inall instances throughout this application and in the appended claims,the amount of F and NO₂ is above 100.00%.

EXAMPLE II

Enamel-forming components 1 and 2 were formed using the lead-free andcadmium-free aluminum phosphate glass frits prepared in Example I by wetmilling the following ingredients (in parts by weight) to a fineness ofless than about 1.0 cm³ being retained from a 50.0 cm³ sample on a 400mesh sieve:

Enamel Enamel Ingredient Component 1 Component 2 Glass Frit A 100.0 80.0Glass Frit B 0 20.0 TiO₂ 10.0 6.0 F 6340 Black Oxide 0 8.0 Pigment(FERRO) KOH 1.5 1.05 Sodium Metasilicate 1.5 0.25 Water 50 50

EXAMPLE III

A fluorocarbon polymer component was prepared by dispersing 60.0 gramsof polytetrafluoroethylene powder purchased from DYNEON as TF 9207 in40.0 grams of water using 0.5 grams of a perfluorinated alkyl salt as adispersing agent. The polytetrafluoroethylene powder had an averageparticle size of about 4.0 μm.

EXAMPLE IV

Compositions A and B were formed by mixing the enamel-forming componentsprepared in Example II with the fluorocarbon polymer component preparedin Example III using a mixer as follows:

Ingredient Composition A Composition B Enamel-Forming Component 1 100 g. 0 Enamel Forming Component 2  0 100 g. Fluorocarbon Polymer Component 30 g.  30 g.

EXAMPLE V

An aluminum frying pan (diameter 28 cm, thickness 3 mm) was degreasedusing an alkali washing liquid. Composition A from Example IV wasapplied to the aluminum cooking surface of the frying pan by wetspraying using a conventional spray gun (orifice diameter 0.5-0.8 mm) atthe rate of about 100-150 g/m². The sprayed aluminum frying pan was thenplaced in an oven at a temperature of about 80-100° C. for about 7minutes to dry the composition. The sprayed aluminum frying pan was thenplaced into an oven at a temperature of about 500° C. for about 10minutes to sinter the applied coating. After sintering, the aluminumfrying pan was removed from the oven and allowed to cool to roomtemperature. The applied sintered coating had a smooth, dark greyappearance. The thickness of the applied sintered coating wasapproximately 50 μm.

The coated surface of the aluminum frying pan was tested for acidresistance according to ISO 2722, hardness on the Mohs scale, easinessto clean according to the Easy-To-Clean Test (FAN Procedure), andscratch resistance in accordance with the Scratch-Resistance Test (NEN2713). The results of these tests are reported below together with theresults of tests performed on a conventional polytetrafluoroethylenecoating (in all tests, the conventional polytetrafluoroethylene coatingwas a stratified coating containing pigments and coating hardenerspresently available on cookware sold in the commercial hollowaremarket):

Test Score for Coating Score for PTFE Mohs Hardness  6  1 AcidResistance AA AA Easiness to Clean 25 25 Scratch Resistance  4.0 N  2.1N

Visual inspection of the frying pan following the Easy-To-Clean Testrevealed that the tested surface was hardly stained.

EXAMPLE VI

Composition B from Example IV was applied by wet spraying using aconventional spray gun at a rate of about 100-150 g/m² to a firedground-coated sheet steel blank. The sprayed sheet steel blank was thenplaced in an oven at a temperature of about 80-100° C. for about 7minutes to dry the composition. The sprayed sheet steel blank was thenplaced into an oven at a temperature of about 475° C. for about 10minutes to sinter the applied coating. After sintering, the sheet steelblank was removed from the oven and allowed to cool to room temperature.The applied sintered coating had a smooth, dark grey appearance. Thethickness of the applied sintered coating was approximately 60 μm.

The coated surface of the sheet steel blank was tested for acidresistance according to ISO 2722, hardness on the Mohs scale, easinessto clean according to the Easy-To-Clean Test (FAN Procedure), and inaccordance with the Cross Hatched Tape Test (ASTM D-3359-95a). Theresults of these tests are reported below together with the results oftests performed on a conventional polytetrafluoroethylene coating:

Test Score for Coating Score for PTFE Mohs Hardness 5-6  1 AcidResistance AA AA Easiness to Clean 24 25 Cross Hatched Tape 4B 5B

Visual inspection of the coated sheet steel blank following theEasy-To-Clean Test revealed that the tested surface was hardly stained.

EXAMPLE VII

An aluminized steel plate was degreased using alkali washing liquid.Composition A from Example IV was applied to the aluminized surface ofthe steel plate by wet spraying using a conventional spray gun at therate of about 100-150 g/m². The sprayed aluminized steel plate was thenplaced in an oven at a temperature of about 80-100° C. for about 7minutes to dry the composition. The sprayed aluminized steel plate wasthen placed into an oven at a temperature of about 500° C. for about 10minutes to sinter the applied coating. After sintering, the aluminizedsteel plate was removed from the oven and allowed to cool to roomtemperature. The applied sintered coating had a smooth, dark greyappearance. The thickness of the applied sintered coating wasapproximately 50 μm.

The coated surface of the aluminized steel plate was tested for acidresistance according to ISO 2722, hardness on the Mohs scale, easinessto clean according to the Easy-To-Clean Test (FAN Procedure), andscratch resistance in accordance with the Scratch-Resistance Test (NEN2713). The results of these tests are reported below together with theresults of tests performed on a conventional polytetrafluoroethylenecoating:

Test Score for Coating Score for PTFE Mohs Hardness  6  1 AcidResistance AA AA Easiness to Clean 25 25 Scratch Resistance  4.0 N  2.1N

Visual inspection of the coated aluminized steel plate following theEasy-To-Clean Test revealed that the tested surface was hardly stained.

EXAMPLE VIII

Composition B from Example IV was applied by wet spraying using aconventional spray gun at a rate of about 100-150 g/m² to a ceramicshard that had previously been fired at around 1000° C. The sprayedshard was then placed in an oven at a temperature of about 80-100° C.for about 7 minutes to dry the composition. The sprayed shard was thenplaced into an oven at a temperature of about 475° C. for about 10minutes to sinter the applied coating. After sintering, the shard wasremoved from the oven and allowed to cool to room temperature. Theapplied sintered coating had a smooth, dark grey appearance. Thethickness of the applied sintered coating was approximately 50 μm.

The coated surface of the shard was tested for acid resistance accordingto ISO 2722, hardness on the Mohs scale, and easiness to clean accordingto the Easy-To-Clean Test (FAN Procedure). The results of these testsare reported below together with the results of tests performed on aconventional polytetrafluoroethylene coating:

Test Score for Coating Score for PTFE Mohs Hardness 5-6  1 AcidResistance AA AA Easiness to Clean 24 25

EXAMPLE IX

47.5 g. of lead-free and cadmium-free aluminum phosphate glass frit Afrom Example I, 35.0 g. of lead-free and cadmium-free aluminum phosphateglass frit B from Example I, and 7.5 g. powdered mica were dry milledtogether to a fineness of about 1.0% residue being retained on a 400mesh sieve. 17.5 g. of polytetrafluoroethylene powder having an averageparticle size of 4.0 μm was mixed with the previously milledingredients. The mixture was then slowly added to 35.0 g. of pine oiland blended until it had a homogeneous appearance.

The composition was applied by screen printing to surface of an aluminumfrying pan that had previously been coated with Composition A as inExample V. The screen-printed aluminum frying pan was then placed in anoven at a temperature of about 80-100° C. for about 7 minutes to dry thecomposition. The aluminum frying pan was then placed into an oven at atemperature of about 500° C. for about 10 minutes to sinter the appliedscreen-printed coating. After sintering, the aluminum frying pan wasremoved from the oven and allowed to cool to room temperature. Thesintered screen-printed coating had a smooth, copper appearance. Thethickness of the sintered screen-printed coating was approximately 20-30μm.

The sintered screen-printed surface of the aluminum frying pan wastested for acid resistance according to ISO 2722, hardness on the Mohsscale, easiness to clean according to the Easy-To-Clean Test (FANProcedure), and scratch resistance in accordance with theScratch-Resistance Test (NEN 2713). The results of these tests wereidentical to the results reported for the coating in Example V. Visualinspection of the screen-printed frying pan following the Easy-To-CleanTest revealed that the tested surface was hardly stained.

EXAMPLE X

100 parts by weight of lead-free and cadmium-free aluminum phosphateglass frit A from Example I, 13.3 parts by weight of lead-free andcadmium-free aluminum phosphate glass frit B from Example I, and 8.0parts by weight F 6340 Black Oxide Pigment (FERRO) were dry milledtogether to a fineness of about 1.0% residue being retained on a 400mesh sieve. 30 parts by weight of PFA powder having an average particlesize of about 4.0 μm was mixed with the previously milled ingredientstogether with an organopolysiloxane. The resulting powder had a bulkresistivity of about 5×10¹⁵ ohm/cm to about 80×10¹⁵ ohm/cm. Aftermilling, the composition was applied using a standard corona dischargegun at 50 kV to about 100 kV to a 25 cm×25 cm×0.5 mm sheet steel couponthat had previously been coated with a conventional enamel ground coat.The application rate of the dry composition was about 400 g/m². Thesheet steel coupon was then placed into an oven at a temperature ofabout 475° C. for about 10 minutes to sinter the applied coating. Aftersintering, the sheet steel coupon was removed from the oven and allowedto cool to room temperature. The applied sintered coating had a smooth,dark grey appearance. The thickness of the applied sintered coating wasapproximately 40 μm.

The coated surface of the sheet steel coupon was tested for acidresistance according to ISO 2722, hardness on the Mohs scale, easinessto clean according to the Easy-To-Clean Test (FAN Procedure), andscratch resistance in accordance with the Scratch-Resistance Test (NEN2713). The results of these tests are reported below together with theresults of tests performed on a conventional polytetrafluoroethylenecoating:

Test Score for Coating Score for PTFE Mohs Hardness  6  1 AcidResistance AA AA Easiness to Clean 25 25 Scratch Resistance  4.0 N  2.1N

The foregoing examples demonstrate that a coating formed using thecomposition and method according to the invention is substantiallyharder and more scratch-resistant than conventionalpolytetrafluoroethylene coatings, but provides similar non-stick andeasy-to-clean properties.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and illustrative examples shown anddescribed herein. Accordingly, various modifications may be made withoutdeparting from the spirit or scope of the general inventive concept asdefined by the appended claims and their equivalents.

1. A composition for use in forming a single-layer abrasion-resistanteasy-to-clean coating on a substrate, said composition comprising amixture of from about 2.5% to about 50% by weight of a fluorocarbonpolymer component and from about 50% to about 97.5% by weight of anenamel-forming component, said enamel-forming component comprising atleast a first lead-free and cadmium-free glass frit, said firstlead-free and cadmium-free glass frit comprising by weight from about30% to about 50% P₂O₅, from about 15% to about 30% Al₂O₃, and from about2% to about 40% X₂O where X=Na and/or K.
 2. The composition according toclaim 1 wherein said fluorocarbon polymer component comprises one or ablend of polymers and/or copolymers that are either fully or partiallyfluorinated.
 3. The composition according to claim 2 wherein saidpolymers and/or copolymers are selected from the group consisting ofPTFE, modified PTFE, MFA, PFA, HFP, CTFE, FEP, and PVDF.
 4. Thecomposition according to claim 1 wherein said fluorocarbon polymercomponent comprises a dispersion of one or a blend of fluorocarbonpolymers.
 5. The composition according to claim 4 wherein saidfluorocarbon polymer component comprises an aqueous dispersion of one ora blend of fluorocarbon polymers.
 6. The composition according to claim5 wherein said fluorocarbon polymers have an average particle sizewithin the range of from about 50 nm to about 10 microns.
 7. Thecomposition according to claim 1 wherein said first lead-free andcadmium-free glass frit comprises by weight from about 30% to about 50%P₂O₅, from about 15% to about 30% Al₂O₃, from about 2% to about 40% X₂Owhere X=Na and/or K, up to about 12% B₂O₃, up to about 10% ZnO, up toabout 8% SiO₂, up to about 5% Li₂O, up to about 3% MnO, up to about 3%CoO, up to about 3% NiO, up to about 3% CuO, up to about 3% Sb₂O₃, up toabout 3% Fe₂O₃, and up to about 3% MoO₃.
 8. The composition according toclaim 7 wherein said enamel-forming component further comprises a secondlead-free and cadmium-free glass frit, said second lead-free andcadmium-free glass frit comprising by weight from about 30% to about 50%P₂O₅, from about 2% to about 40% X₂O where X=Na and/or K, from about 10%to about 30% Al₂O₃, up to about 12% SiO₂, up to about 8% B₂O₃, up toabout 5% Li₂O, up to about 5% NiO, up to about 4% MnO, up to about 3%CoO, up to about 3% CuO, up to about 3% Sb₂O₃, up to about 3% Fe₂O₃, andup to about 3% MoO₃.
 9. The composition according to claim 8 whereinsaid first lead-free and cadmium-free glass frit and/or said secondlead-free and cadmium-free glass frit further comprises by weight up toabout 15% fluorine above the weight of the other components in the frit.10. The composition according to claim 1 wherein said substratecomprises a material selected from the group consisting of metals,glass, ceramics, and stone.
 11. The composition according to claim 10wherein said metal substrate comprises steel.
 12. The compositionaccording to claim 11 wherein said steel is hot rolled steel, enamelground-coated steel, aluminized steel, pickled nickel-coated steel,stainless steel, or galvanized steel.
 13. The composition according toclaim 10 wherein said metal substrate comprises cast iron.
 14. Thecomposition according to claim 10 wherein said metal substrate comprisesaluminum or cast aluminum.
 15. The composition according to claim 10wherein said metal substrate comprises copper.
 16. The compositionaccording to claim 1 further comprising pigments and/or mill additions.17. The composition according to claim 1 wherein said fluorocarbonpolymer component comprises from about 2.5% to about 30% by weight ofsaid composition.
 18. A composition for use in forming a single-layerabrasion-resistant easy-to-clean coating on a substrate, saidcomposition comprising a mixture of from about 2.5% to about 50% byweight of a fluorocarbon polymer component and from about 50% to about97.5% by weight of an enamel-forming component, said enamel-formingcomponent comprising at least a first lead-free and cadmium-free glassfrit, said first lead-free and cadmium-free glass frit comprising byweight from about 30% to about 50% P₂O₅, from about 15% to about 30%Al₂O₃, from about 2% to about 40% X₂O where X=Na and/or K, up to about12% B₂O₃, up to about 10% ZnO, up to about 8% SiO₂, up to about 5% Li₂O,up to about 3% MnO, up to about 3% CoO, up to about 3% NiO, up to about3% CuO, up to about 3% Sb₂O₃, up to about 3% Fe₂O₃, and up to about 3%MoO₃.
 19. The composition according to claim 18 wherein said firstlead-free and cadmium-free glass frit further comprises up to about 15%by weight F above the weight of the other components in the frit. 20.The composition according to claim 18 wherein said fluorocarbon polymercomponent comprises polytetrafluoroethylene.
 21. A method of forming anabrasion-resistant easy-to-clean single-layer coating on a substratecomprising: providing a substrate; providing a composition comprising amixture of from about 2.5% to about 50% by weight of a fluorocarbonpolymer component and from about 50% to about 97.5% by weight of anenamel-forming component, said enamel-forming component comprising atleast a first lead-free and cadmium-free glass frit, said firstlead-free and cadmium-free glass frit comprising by weight from about30% to about 50% P₂O₅, from about 15% to about 30% Al₂O₃, and from about2% to about 40% X₂O wherein X=Na and/or K; applying said composition tosaid substrate; and sintering said applied composition to fuse saidcoating to said substrate and thereby form the abrasion-resistanteasy-to-clean single-layer coating thereon.
 22. The method according toclaim 21 wherein said composition is applied to said substrate by anapplication technique selected from the group consisting of wetspraying, screen printing, electrophoresis, dry electrostaticdeposition, wet dipping, and flow coating.
 23. The method according toclaim 21 wherein said substrate comprises a material selected from thegroup consisting of metals, glass, ceramics, and stone.
 24. The methodaccording to claim 21 wherein said sintering is accomplished by heatingsaid applied composition to a temperature of from about 400° C. to about580° C. for about 2 to about 25 minutes.
 25. The method according toclaim 21 wherein said fluorocarbon polymer component comprises one or ablend of polymers and/or copolymers that are either fully or partiallyfluorinated.
 26. The composition according to claim 25 wherein saidpolymers and/or copolymers are selected from the group consisting ofPTFE, modified PTFE, MFA, PFA, HFP, CTFE, FEP, and PVDF.
 27. The methodaccording to claim 21 wherein said first lead-free and cadmium-freeglass frit comprises by weight from about 30% to about 50% P₂O₅, fromabout 15% to about 30% Al₂O₃, from about 2% to about 40% X₂O where X=Naand/or K, up to about 12% B₂O₃, up to about 10% ZnO, up to about 8%SiO₂, up to about 5% Li₂O, up to about 3% MnO, up to about 3% CoO, up toabout 3% NiO, up to about 3% CuO, up to about 3% Sb₂O₃, up to about 3%Fe₂O₃, and up to about 3% MoO₃.
 28. The method according to claim 27wherein said enamel-forming component further comprises a secondlead-free and cadmium-free glass frit, said second lead-free andcadmium-free glass frit comprising by weight from about 30% to about 50%P₂O₅, from about 2% to about 40% X₂O where X=Na and/oil K, from about10% to about 30% Al₂O₃, up to about 12% SiO₂, up to about 8% B₂O₃, up toabout 5% Li₂O, up to about 5% NiO, up to about 4% MnO, up to about 3%CoO, up to about 3% CuO, up to about 3% Sb₂O₃, up to about 3% Fe₂O₃, andup to about 3% MoO₃.